The present disclosure relates to a developing device configured to develop an electrostatic latent image on an image carrier by causing the image carrier to hold toner, and an image forming apparatus including the developing device.
An image forming apparatus such as a copying machine or a printer which forms an image on a paper sheet by electrophotography is provided with a developing device. The developing device develops with toner an electrostatic latent image formed on an image carrier such as a photosensitive drum. As a developing method, there has been known a so-called two-component developing method in which a two-component developer composed of magnetic carrier and toner is used to develop a toner image on the image carrier. As one example of the two-component developing method, the following method is known: by use of a magnetic roller provided with a magnet inside thereof and a developing roller arranged so as to be separated from an image carrier by a predetermined gap, only the toner, which is nonmagnetic, is transferred onto the developing roller with the magnetic carrier remaining on the magnetic roller, to form a thin toner layer on the developing roller. Then, the toner is caused to fly to be attached to the electrostatic latent image on the image carrier, from the developing roller in an AC electric field.
In such a typical developing device, in order to convey the toner by a constant amount to a position opposed to the developing roller, a regulation blade is provided which regulates a developer layer to be formed on the surface of the magnetic roller. The regulation blade is arranged on the upstream side in the rotation direction of the magnetic roller during development, relative to a position where the developing roller and the magnetic roller oppose each other.
When the toner is transferred from the developing roller to the image carrier, or when the toner is transferred from the magnetic roller to the developing roller, a part of the toner scatters within a housing of the developing device. A part of the scattered toner attaches to surfaces of the regulation blade, in particular, to a surface thereof turned toward the position where the developing roller and the magnetic roller oppose each other. When the toner attached and accumulated on the surfaces of the regulation blade comes off from the regulation blade and moves to the vicinity of the developing roller or the image carrier, the toner layer on the developing roller is disturbed or the amount of toner held on the developing roller varies. Due to influence of the accumulated toner, an excessive amount of toner is supplied to the image carrier. This may cause a risk of lowered quality of an image to be formed, resulting in poor image.
With regard to this, as a typical method for collecting the toner accumulated on the regulation blade, there is known a method in which magnetic poles provided inside the magnetic roller are rotated.